Dead dinos no help to emerging mammals

Challenging conventional wisdom

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The triumphant rise of the mammals had nothing to do with the extinction of the dinosaurs, according to new research, published in the journal Nature.

The paper's co-author, Kate Jones, told BBC Radio 4: "The meteor impact that killed off the dinosaurs has traditionally been thought to have given mammals the edge they needed."

The text book theory goes that with the dinosaurs gone, the mammals suddenly had an embarrassment of ecological niches to exploit and roles to evolve into. But with the new family tree, this conventional wisdom is being called into question.

Boffins at the Zoological society in London, including Jones, have rebuilt a mammalian family "supertree", showing when and where various groupings of mammals emerged. Their evidence, which draws on several peer reviewed studies, shows that mammals had begun to diversify long before the extinction of the dinosaurs.

The work shows that the major subgroupings of placental mammals emerged 93 million years ago, some 28 million years before the impact thought most likely to have killed off the giant lizards.

They remained quite static in their existence, the rate of evolution falling back, until 10 million years or so after the dinosaurs left the building. The beginning of this epoch, called the Eocene, was characterised by a period of extremely fast warming: geological evidence suggests the global temperature rose by six degrees in a thousand years or less.

However, Dr Rob Asher, an expert on mammalian phylogeny at the University of Cambridge, told the BBC that the idea of a sudden extinction of dinosaurs and subsequent flourishing of mammals is something of a straw man.

"Palaeontologists have known for over a hundred years that not all modern placental mammal groups appear right after the K-T boundary. Most orders of placental mammals - what I mean by that is cats and bats and whales and people - appear at the Eocene. On the flipside, not all dinosaurs disappear at the end of the Cretaceous," he said. ®